The invention relates to the carburizing of metal melted down from scrap metal, particularly steel scrap, prereduced iron sponge, pellets, and the like. The invention is particularly applicable in connection with the method described in U.S. Pat. application Ser. No. 237,158, now U.S. Pat. No. 3,788,837 issued to the present inventors. The patent describes a method of melting scrap iron comprising the steps of maintaining a charge of particulate scrap iron in an upright elongated melting chamber comprising a bottom wall; contacting a lower portion of the charge with a disc-shaped flame produced from an oxygen fuel mixture, said flame being spread transversely through said melting chamber and being arranged upwardly of said bottom wall so that the metal of said charge melts and flows onto said bottom wall thereby becoming interposed between said flame and said bottom wall and protecting the latter from the former; and continuously discharging the melted metal from said melting chamber. The flame can be injected into the charge either by a burner or the like disposed centrally of the charge or in an annular zone provided with burners or the like peripherally of said charge.
It is a difficulty of this earlier process that the liquidus point of the resulting melt is only a little below the actual temperature of the melt discharged from the melting chamber. This situation leads to the danger of freezing up and the formation of "bears", because of losses of heat which are usually unavoidable in the melt receiving and retaining zone when the melt is stored or transported therein over some extended period of time. In some cases liquid pig iron has been mixed with the melted scrap in order to lower the liquidus point by carbon contained in the pig iron, but such admixture is not always possible. Other methods of carburizing the iron are therefore desired. In other processes caburizing is achieved by dropping particulate carbon onto a melt in a melt receiving or retaining vessel. However, in the melting down of particulate iron, especially as described in the aforementioned patent, ferrous oxide slag is formed as part of the liquid iron slag, as particulate iron is melted in the presence of air. Such slag floats on the liquid iron and prevents particulate carbon from sinking into the liquid iron. The particulate carbon would float on or in the slag, would be coated thereby and sintered therein, and would not come into such direct contact with the liquid metal as is necessary for the carburizing of the metal.